1. Field of the Invention
The present invention relates generally to a backside illumination (BSI) CMOS image sensing process, and more specifically to a backside illumination (BSI) CMOS image sensing process that forms curved mirrors on an active side of a substrate.
2. Description of the Prior Art
Back side illumination (BSI) image sensors are popular image sensors in the present industry. Back side illumination (BSI) image sensor fabrication can be integrated into conventional semiconductor processes, and therefore back side illumination (BSI) image sensors have advantages of low cost, tiny size, and high integration. Back side illumination (BSI) image sensors also have advantages of low operating voltage, low power consumption, high quantum efficiency, low read-out noise, and random access. Therefore, back side illumination (BSI) image sensors are adopted broadly in electronic products, such as PC cameras and digital cameras.
A conventional back side illumination (BSI) image sensor structure can be divided by function into a light sensing area and a peripheral electronic circuit area. The light sensing area has a plurality of photodiodes arranged in an array, and MOS transistors to detect the light intensity, i.e. a reset transistor, a current source follower and a row selector. The peripheral electronic circuit area connects interconnects to external connections. A principle function of the back side illumination (BSI) image sensor is to divide incident beams into combinations of light with different wavelengths. The light is received by a plurality of imaging devices on the semiconductor substrate and transformed into digital signals of different intensity. For instance, an incident beam is divided into a combination of red, green and blue light and received by corresponding photodiodes. Each photodiode transforms the light intensity into digital signals.